The long-term goal of this research is to understand how somatosensory information is processed dynamically during purposeful hand movements. The experiments are designed to demonstrate when, and under what behavioral conditions, the responsiveness of primate sensorimotor cortical neurons is altered. This work is also designed to determine what behavioral consequences result from these alterations. Through neurophysiological experiments, we will determine how sensory responses and movement-related activity is altered during three types of behaviors that mimic those used everyday. The first is designed to show how sensory responsiveness changes immediately following an unpredictable outcome of a previous movement. The second will show how responsiveness changes when somatosensory inputs are needed to guide movements as compared with guidance by explicit visual cues. The third will determine if somatosensory signals can be detected at times before movements when sensory gating is thought to occur, and if this detection depends on the modality of stimuli previously used to trigger movements. Each experiment will determine the conditions under which the activity of sensorimotor cortical neurons is more tightly coupled to sensory stimuli and movement kinematics. The hypotheses to be tested are: (1) That the responsiveness of sensorimotor cortical neurons is attenuated when behavioral conditions are predictable. (2) That facilitation and suppression of responsiveness occur when peripheral and central inputs are crucial for the initiation and execution of movements, and that these modulations are regionally-specific. (3) That overly-trained movements can be altered only up to a certain point before their onset, and that this phenomenon reflects transient sensory gating which can be seen in the activity of sensorimotor cortical neurons. The underlying hypothesis is that external sensory information is utilized more when there has been a mismatch between actual and predicted behavioral outcome. These hypotheses will be tested, using single electrodes and multi-electrode arrays to record extracellular activity in the primary somatosensory, parietal (area 5), primary motor and premotor (PMd) cortices of awake, behaving monkeys trained to perform wrist movement tasks. Coupling of activity to sensory stimuli will be assessed by mean vector analyses. Movement kinematics will be correlated with neuronal activity using multiple regression analyses. The three behaviors to be studied are similar to those used during retraining when sensory disorders occur following stroke, traumatic head injury, peripheral neuropathy and movement disorders. By understanding how and where somatosensory responsiveness is modified during behavior, deficits can be more readily assessed and localized.